Current methods of encapsulating electronic devices exhibit one or more disadvantages, including; (1) the inability to predictably define the outer perimeter of the encapsulant, (2) the use of a time-consuming thermal hardening process, or (3) the inability to meet the dimensional packaging requirements of todays small, densely packed hybrid circuits.
U.S. Pat. No. 3,381,071 to C. W. Logan et al shows an electronic circuit encapsulated in a thermally cured encapsulant such as an epoxy resin. The encapsulant is formed by first screen-printing a barrier wall comprising a thermally curable material such as glass onto a ceramic substrate. The barrier wall is thermally cured, and the electronic device is mounted on the substrate within the barrier. The epoxy resin is deposited, in liquid form, over the electronic device and is contained within the barrier wall. The encapsulant is then cured through a second application of heat.
The process shown in C. W. Logan et al suffers from several disadvantages, the first being that the heat curing of the barrier wall necessarily results in some spreading of the wall, decreasing the compactness of the resulting encapsulated device. The second disadvantage is that the thermal curing of the encapsulant is very time consuming, taking, as described in the patent, 24 hours.
U.S. Pat. No. 4,203,792 to Thompson shows a method for encapsulating electronic devices using a multicomponent polymer material comprising a mixture of a minor amount of a radiation curable material with a major amount of a thermally curable material. After depositing the encapsulant over the electronic device, the encapsulant is radiatively cured for a short period of time to establish its shape. The encapsulant is subsequently heat cured to form the finished device. The process shown in Thompson suffers from the disadvantage of requiring a complex curing process including both a radiation curing stage and a heat curing stage.
U.S. Pat. No. 4,635,356 to Ohuchi et al shows a method of encapsulating an electronic device wherein a large, preformed spacer is used as a barrier wall to surround electronic components mounted on a radiation-transparent support board. The area within the barrier wall is filled with an encapsulant comprising a radiatively curable material. The encapsulant is cured by exposure to radiation through the support board, and the barrier is removed to form the finished device. Ohuchi et al suffers from the disadvantage that the preformed barrier wall is time consuming to place and remove, and requires a substantial amount of space.
It would thus be desirable to provide an encapsulated electronic device, and a method of forming the same, wherein the outer perimeter of the encapsulant and hence the shape of the encapsulant could be closely controlled. It would be further desirable if the process of forming such a device could be performed relatively faster than the thermal curing processes described in the background above.